AION/Magis

Abstract:

A first measurement of the polarization of W bosons with large transverse momenta in pp collisions is presented. The measurement is based on 36pb⊃-1 of data recorded at √s=7TeV by the CMS detector at the LHC. The left-handed, right-handed, and longitudinal polarization fractions (f L, fR, and f0, respectively) of W bosons with transverse momenta larger than 50GeV are determined by using decays to both electrons and muons. The muon final state yields the most precise measurement: (fL-fR)⊃-=0.240±0.036(stat)±0.031(syst) and f0-=0.183±0.087(stat)±0.123(syst) for negatively charged W bosons and (fL-fR)⊃+=0.310±0.036(stat) ±0.017(syst) and f0+=0.171±0.085(stat)±0.099(syst) for positively charged W bosons. This establishes, for the first time, that W bosons produced in pp collisions with large transverse momenta are predominantly left-handed, as expected in the standard model. © 2011 American Physical Society.

Abstract:

We study the suitability of correlator product states for describing ground-state properties of two-dimensional spin models. Our ansatz for the many-body wave function takes the form of either plaquette or bond correlator product states and the energy is optimized by varying the correlators using Monte Carlo minimization. For the Ising model we find that plaquette correlators are best for estimating the energy while bond correlators capture the expected long-range correlations and critical behavior of the system more faithfully. For the antiferromagnetic Heisenberg model, however, plaquettes outperform bond correlators at describing both local and long-range correlations because of the substantially larger number of local parameters they contain. These observations have quantitative implications for the application of correlator product states to other more complex systems, and give important heuristic insights: in particular the necessity of carefully tailoring the choice of correlators to the system considered, its interactions and symmetries.